Yellow Crazy Ant Risk Assessment
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Invasive animal risk assessment Biosecurity Queensland Agriculture Fisheries and Department of Yellow crazy ant Anoplolepis gracilipes Steve Csurhes and Clare Hankamer First published 2012 Updated 2016 © State of Queensland, 2016. The Queensland Government supports and encourages the dissemination and exchange of its information. The copyright in this publication is licensed under a Creative Commons Attribution 3.0 Australia (CC BY) licence. You must keep intact the copyright notice and attribute the State of Queensland as the source of the publication. Note: Some content in this publication may have different licence terms as indicated. For more information on this licence visit http://creativecommons.org/licenses/ by/3.0/au/deed.en" http://creativecommons.org/licenses/by/3.0/au/deed.en Front cover: Anoplolepis gracilipes at sugar bait (Lautoka, Fiji) Photo: Sarnat (2008), used with permission Invasive animal risk assessment: Yellow crazy ant Anoplolepis gracilipes 2 Contents Summary 4 Introduction 5 Identity and taxonomy 5 Nomenclature 5 Description 6 Reproduction and dispersal 8 Diet 9 Origin and distribution 10 Preferred habitat 11 History as a pest elsewhere 12 Use 14 Pest potential in Queensland 15 Current impact in Australian territory 15 Christmas Island 15 Cocos (Keeling) Islands 15 Northern Territory 16 New South Wales 16 Western Australia 16 Current distribution and impact in Queensland 16 Potential distribution and impact in Queensland 18 Likelihood of additional incursions 20 References 21 Invasive animal risk assessment: Yellow crazy ant Anoplolepis gracilipes 3 Summary Anoplolepis gracilipes is commonly known as the yellow crazy ant because of its colour and frantic behaviour when disturbed. While its origin is obscure, there is increasing evidence that it is native to South-East Asia. Yellow crazy ants are readily dispersed in sea cargo, especially timber, and have achieved a pantropical distribution as a consequence of global trade. The yellow crazy ant has been included among 100 examples of the world’s worst invasive species by the International Union for Conservation of Nature. It has naturalised in numerous places, especially tropical islands, across the world. On Christmas Island, yellow crazy ants are decimating the island’s iconic red land crabs. A significant population also exists in the Northern Territory. Yellow crazy ants were first detected in 2001 in Cairns. Since then, more than 20 additional sites have been found, in and around Cairns, Townsville, Hervey Bay, Caboolture and Brisbane. The total area of infestation involves at least 320 hectares. Populations at some of these sites have been eliminated, whereas others are subject to ongoing control. This pest risk assessment presents evidence that yellow crazy ants have the potential to become a significant pest in Queensland. Climate modelling suggests the species could spread across substantial areas. Habitats most at risk are offshore islands with dense forest, monsoon forest/rainforest and plantations along the tropical east coast (generally shady, moist habitats). Negative impacts are likely to include indirect damage to fruit caused by the ants’ tendency to protect various scale insects, loss or decreased abundance of native ant species, and predation of a wide range of invertebrates and small vertebrates, resulting in a general decline in biodiversity. Invasive animal risk assessment: Yellow crazy ant Anoplolepis gracilipes 4 Introduction Identity and taxonomy Speciec s Anon plole pip s grg a cic lipes Smith SyS nonyms Anooplolepis llongipes Jerdon Anooplolepis (Ano oplolepis) llongipes Jerdon Anon plole pip s trifa cic ata Smith Anon plole pip s trifas cic ata Smith Formica grg a cic lipes Smith Foro mica lonl gipes Jerdon Formicm a trifasciata Smith Oece ophylla lonl gipes Jerdon Plagiolel pis gr aca i lipl es Smith Plagiiolepis (Anoplolepis) longipes Jerdon Plagiiolepis longipes Jerdon Pllogiolepis (Ano oplolepis) llongipes Jerdon Prenon le pip s grg a cic lipes Smith Coommon names Yellow craz y ant , craz y an t (English) , graman g an t (Indonesian Bahasa), long-legged ant (English), Maldive ant (English, Seyc chelles) Sources: Antbase (2010); GISD (2009); Harris and Berry (2010). Family: Formicidae (sub-family: Formicinae) Nomenclature While the preferred scientific name is Anoplolepis gracilipes, much of the literature uses its synonym Anoplolepis longipes (ITIS 2010; GISD 2009). It is questionable whether the yellow crazy ant should be included in the genus Anoplolepis. Even though the centre of diversity for Anoplolepis is in Africa, there is a growing body of evidence that the yellow crazy ant is native to South-East Asia. There is a possibility that the yellow crazy ant will be split from the Anoplolepis genus in a similar manner to Paratrechina longicornis, which is now recognised as a monotypic genus (LaPolla et al. 2010; B Hoffmann, CSIRO, pers. comm. 2010). There is evidence of intraspecific variation. Based on mitochondrial DNA analysis of yellow crazy ants from the Tokelau Archipelago, Abbott et al. (2007) revealed the presence of two haplotypes (Type A and Type D). Haplotype D was more aggressive, invasive and able to displace a higher proportion of other ant species (50 per cent fewer ant species were found on Invasive animal risk assessment: Yellow crazy ant Anoplolepis gracilipes 5 islands invaded by haplotype D). The authors concluded that, contrary to previous evidence for invasive ant species where environmental factors were thought to play a key role, genetic characteristics may be equally or more important to invasion success. Description Yellow crazy ants are brownish-yellow or yellow-orange and 1–5 mm long (Figures 1 and 2). Figure 1. Yellow crazy ant (Anoplolepis gracilipes) (Photo: Sarnat (2008), used with permission) Figure 2. Yellow crazy ants defending their nest Invasive animal risk assessment: Yellow crazy ant Anoplolepis gracilipes 6 Workers have uniform morphology (Holway et al. 2002), with a long slender body and a gaster that is usually darker than the head and thorax. The gaster is armed with an acidopore and erect hairs are present. A sting is absent (Abbott et al. 2005). The species has a characteristic erratic walking style when disturbed, an attribute leading to its colloquial name ‘crazy ant’. Also known as the long-legged ant, yellow crazy ants are noted for their remarkably long legs and antennae—the antennal scape length is more than 1.5 times the head length and is a key diagnostic feature (Figure 3). Antennae have 11 segments, including the scape. Figure 3. Long antennal scapes of Anoplolepis gracilipes (Photo: Sarnat (2008), used with permission) The body is relatively long, compared to other ants, and incorporates a long ‘neck’ attaching the head to the thorax. It has a single waist segment—the petiole—which is thick and raised (with an inverted U-shaped crest), not flat (Wikipedia 2010a). Themesosoma , or alitrunk, (the first three thoracic segments and the first abdominal segment) is slender and lacks hairs on the dorsum. The pronotum (the dorsal portion of the prothorax, the first of the three thoracic segments which bears the first pair of legs) is narrow, with an almost straight dorsum in profile. The anterior portion of the mesonotal dorsum, back to the propodeum, is gently concave in profile. The propodeal dorsum is convex in profile (Wikipedia 2010a). Spines are absent on the propodeum (Abbott et al. 2005). The head is oval, with large convex eyes and erect hairs. The mandibles have eight ‘teeth’ each and the clypeus is produced medially with a convex anterior margin, without longitudinal carinae (narrow, raised ridges) (Abbott et al. 2005). The following species might be confused with the yellow crazy ant: • other genera of Formicinae in Australia that have antennae with 11 segments, namely Acropyga, Plagiolepis and Stigmacros. Yellow crazy ants can be distinguished from these genera by their larger size, longer legs and scapes and yellow colour (CSIRO 2010) • Wasmannia auropunctata, which also has 11 antennae segments, but the last is enlarged into a distinct club. It is smaller than the yellow crazy ant and has a painful sting—hence its name ‘electric ant’ or ‘little fire ant’ (Wikipedia 2010a) Invasive animal risk assessment: Yellow crazy ant Anoplolepis gracilipes 7 • yellow tyrant ant (Iridomyrmex pallidus), which is native to open habitats in northern Australia and very common and similar in size and colour to yellow crazy ants. The latter can be distinguished by the length of the antennae, which extend far above the head, whereas the antennae of I. pallidus barely exceed the head. I. pallidus also has a larger heart-shaped face, bites when disturbed and exudes an extremely strong smell when crushed, unlike yellow crazy ants (TERC 2004) • the genera Leptomyrmex and Oecophylla, which are both similar in size to the yellow crazy ant and have similarly long legs. Yellow crazy ants can be distinguished by a circular opening (acidopore) at the tip of the gaster, whereas Leptomyrmex has a slit-shaped opening (CSIRO 2010; Sarnat 2008). Leptomyrmex rufipes (red spider ant), found in Brisbane Forest Park, has an orange-black body with a black gaster and tends to forage alone (Brisbane Insects and Spiders 2010). Yellow crazy ants can be distinguished from Oecophylla by their more compact petiole (Sarnat 2008). Oecophylla smaragdina (green tree or weaver ant) is native to Australia and its body is elongate and pale yellow or green in colour. Its nests are arboreal and made of leaves stitched together with silk produced by the larvae (CSIRO 2010) • Paratrechina longicornis (crazy ant/black crazy ant/slender crazy ant/hairy ant), which is known for its erratic behaviour, much like yellow crazy ants. It is also invasive and exists in Australia. It is smaller (2.5 mm) than yellow crazy ants and has numerous thick, paired hairs over its entire body, an impressed mesosoma and is black (Sarnat 2008) • some species of Camponotus that are similar in overall size and shape to yellow crazy ants.